This invention relates to apparatus for handling material sampled from geological formations.
During the drilling of bore holes as, for example, in the oil and gas industry, core samples are cut from the formation being drilled to obtain data. Such samples are commonly taken at the bottom of a bore hole during the drilling process by a core barrel which conventionally comprises a rigid outer tube disposed in the drill string above a core bit, and a thin flexible inner assembly located inside the outer tube. The drill string is lowered to the bottom of the well where the rotation of the string, downward force and fluid drives the core bit into the formation so that a core of the formation is forced into the outer tube and inner assembly. Core retainers usually in the form of spring catchers or fingers extend into the inner bore to trap it in place. The entire drilling assembly is then withdrawn from the hole to enable the core to be recovered and cut into suitable lengths for further study.
The handling procedures to recover the string and to cut the core into lengths involve stress and damage to the core, particularly in sandy formations, and this can reduce the value of the data recoverable.
According to the present invention there is provided apparatus for handling a geological sample, the apparatus comprising a container for receiving the sample and having at least one wall with a surface which can change its configuration in response to pressure changes.
The surface of the wall is preferably formed by a covering having trapped pockets of fluid, typically compressible fluid and preferably gas bubbles, which are trapped within a suitable matrix of, for example, foam or plastic. A suitable material for this purpose is conventionally available xe2x80x9cbubble wrapxe2x80x9d which comprises a layer of plastic sheet having gas-filled pockets formed thereon and held captive on the sheet. The pockets are flexible and at normal atmospheric pressure they are slightly turgid extending proud of the surface of the sheet by the volume of the gas trapped inside them. At higher atmospheric pressures the gas inside the pockets is compressed to a lower volume and the pockets are more flaccid, conforming more to the flat sheet.
The covering can be disposed over the whole surface of the container, or can be provided in discrete areas. The covering is preferably resilient and can adopt different configurations.
The container is preferably hollow, with the covering disposed on the inner surface. Alternatively, the container can have the covering disposed on an outer surface as long as it can bear against the core sample when in the container.
The container is preferably in the form of an open-ended cylinder.
The apparatus can be incorporated into a drill or coring string with a drill or coring bit.
The apparatus may incorporate an outer coring barrel around the container, or the container may itself serve as the outer coring barrel.
The covering can optionally comprise a high porosity and impermeable material that can be disposed on or attached to, or can be integral with the inner wall of the container. The covering may also be adapted to reduce friction coefficients, typically on the surface which in use contact the sample.
The expandable surface protects and supports the geological sample (eg the core) at the end of coring process while approaching the surface during the trip out of the hole. When expanded under atmospheric conditions, the surface reduces the diameter of the bore below the diameter of the core bit. When the apparatus enters the bore hole, the naturally increasing hydrostatic pressure applied by the drilling fluid (and/or optionally artificially applied increasing wellbore pressure from surface) will compress the surface and enlarge the inner diameter of the container so that when the apparatus reaches the formation to be sampled, the surface has compressed to leave a space in the container larger than the core to be cut by the core bit. The core can therefore be cut without the surface presenting any, or only minimal, obstacle to the core entering the container.
While pulling out of the hole the hydrostatic pressure on the apparatus will decrease, and the surface will expand to bear against the core trapped in the container, so as to isolate it from jars and other stress encountered during the extraction process which tend to affect the core""s integrity.
The invention also provides a method of handling a geological sample, the method comprising;
providing a container for receiving the sample, the container having a surface which is capable of changing its configuration in response to pressure changes;
introducing the sample into the container;
changing the configuration of the surface to contact the sample; and
withdrawing the container from the formation.
The method can be carried out downhole or on surface.
The method can usefully be carried out at surface, wherein a core can be held in the container having the foam, for example, on its inner surface while in a pressure vessel at an artificially lowered pressure, so that the foam expands and supports the core during handling or cutting of the container into lengths. The invention therefore encompasses such a pressure vessel in combination with the apparatus of the first aspect.